hey guys i was wondering if any of you can give advice on how i can make a cold air intake for my 89 gti cause not many companies make one as you all know im sure. and the ones that do are pretty expensive so any advice on it i would definitely appreciate! thanks

it's not all that hard to fabricate something better than the stock induction set. the stock intake tubes are old enough that they are pretty rotted out so almost anything else you come up with is an upgrade.

the maf on the twincam is, in reality, a hot wire anemometer. it wants to see laminar flow which would mean that you would want the pipe leading up to the measurement point to be 9 times the diameter of the pipe.

the suzuki boys used a helmholtz resonator tucked behind the right side inner fender as a "quieting" box for air flow, introduced it into the filter housing at a point that would induce swirling air in front of the filter media, and let the concentric pleats in the filter straighten out air flow just before it enters the maf.

working outside of the constraints of manufacturing where every piece is made to be compatible with every car they produced and the constant push to save half a penny on each unit, you can build an induction set that's actually an improvement over the oem box.

I hate to point this out, but of all the setups mentioned, only the stock, unmodified system is actually a cold air intake (CAI) because it pulls air from the fender, outside the engine compartment.

All of the other mods pull air from inside the engine compartment, where it is warmer.

I had no idea that the horse snorkel in the fender was actually a helmholtz resonator or that it did anything other than keep water and debris out of the filter and suppress noise--while restricting flow. Certainly the motor sounds better with it gone.

The best setup would be to run the piping all the way through the fender or the metal guard in front of the motor and find somewhere to put the airbox and filter out there. That's the hard part--I can't find a good filter that will fit in the fender or anywhere else I could run hose to.

I hate to point this out, but as soon as the vehicle is moving, the temp at the filter becomes ambient so it makes no difference.

I really didn't hate to point that out. I quite enjoyed it.

Tommy, you're not only still gay, but you're still wrong. A cheap (but effective) cone filter is less than half the price of a drop in K&N, and a real K&N cone filter is about the same. So if you have at least half a brain, you make your own adapter, and get the best of both worlds. Cheap, and fast. Just like your mom.

apparently it needs repeatedly stated that unless the car is sitting still, the under hood temps will be at ambient air temp.

ram air intakes are a load of crap, too.

lessening the wall effect by using smooth tubing and decreasing flow restriction by straightening bends and changing air filters is effective engineering when trying to improve the induction setup.

the factory's plastic induction system that's stashed between the inner and outer fender was designed to: 1. provide a "quieting" chamber so that air pressure at the inlet remained constant 2. provide a feature that allowed water droplets to be separated from inlet air before they could be inducted and 3. utilize a helmholtz resonator to silence the induction noise (the gt parts book even lists the helmholtz resonator as the silencer.)

while the factory engineering and parts production were super, the length of the entire induction set and all of the bends in it are flow killers. i pull all that plastic crap and the formed steel bracket for it out to make room for neater stuff.

I hate to point this out, but as soon as the vehicle is moving, the temp at the filter becomes ambient so it makes no difference.

I really didn't hate to point that out. I quite enjoyed it.

Tommy, you're not only still gay, but you're still wrong. A cheap (but effective) cone filter is less than half the price of a drop in K&N, and a real K&N cone filter is about the same. So if you have at least half a brain, you make your own adapter, and get the best of both worlds. Cheap, and fast. Just like your mom.

what part of the effectiveness of my advice expired in 2006 did you miss?

although it may have been proven wrong since then, it was fact and truth before then.

everyone knows the sun revolves around the earth. Get over it.

On a serious note tho: My car never ran right with a cone filter, or a setup that had a cone filter in the fender. It always ran best with the k&n and open front. My best times were sans filter although it was a whore getting it to idle.

science aside, sometimes the way each car reacts to the expected improvement based on science is suprising.... it doesn't always play out that way. Oh, and one more thing: I had a couple hundred timeslips to support my setup...

_________________2018: The year that'll be shrouded in mystery, mainly because

I love this thread.however (there is always a however)...the percentage improvement in engine efficiency or power could only be measured on a dyno. Seriously.... How can you feel a 2-5% gain in power in such a small engine? The improvement in induction noise would definitely be able to be "measured".

I read a post here years ago where one of our brethren (from Argentina I recall) flow benched a head with different combinations of air filter. and if I recall, he summarised that there is no difference in flow from using a stock filter assembly and any other variant. His observations were that the rest of the air ducting (throttle body etc) was the restrictive component.

HOWEVER.... (another one) in an online magazine called Autospeed, some well positioned owner of an Audi, showed appreciable gains in changing out the stock air ducting with "plastic toilet pipe".... the gains being measured on a dyno. equated to about 5% better performance. Then again, Audi's do not have a MAF sensor that is prehistoric.

toss that one into the fire and see what sparks....

_________________Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car.HP is how fast you hit the wall, torque is how much you push the wall out.

Half the intent was just to make it easier to remove the air filter entirely for racing--the elbow got in the way and made it necessary to loosen everything from the bracket. I also figure that more open can't hurt and now I can see how dirty my air filter is. I do have to change it more frequently like this.

As for the bracket I am not sure if removing it is legal per my scca rules

Nobody that's got the money for dyno time is going to spend it on figuring out how much difference there is between stock, cut-up or various aftermarket air filter setups. For now I'll have to go with TGstring and his timeslips and just remove mine when I'm competing.

The next project is to get some more robust hose to the intake, now that I have successfully dodged having to register the car in CA (we're military so it's not shady, it's a privilege). The irony is that I know the car is extremely clean at the tailpipe, but only in CA do they care whether everything's got stupid CARB stickers on it. It is probably registerable here, but not until being ground through the unnecessary bureaucracy a couple of times first

because i have a highly senstive and finely calibrate dyno in my butt!

Dynobutt. I should have guessed.... sigh....

_________________Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car.HP is how fast you hit the wall, torque is how much you push the wall out.

this is my set up, in the built stageused the foam filter, removed the back and glued the foam and net into the stock part with high temp silicone, and then put in the other half of the stock filter housing, the car pulls great, and i can ear it sucking the air

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